Piezoelectric/electrostrictive device and method of producing the same

ABSTRACT

A piezoelectric/electrostrictive device includes a base  11  having a pair of movable parts  11   a,    11   b  opposing each other and a connecting part  11   c  that connects movable parts  11   a,    11   b  with each other at one end thereof as well as piezoelectric/electrostrictive elements  12   a,    12   b  disposed on the side surfaces of movable parts  11   a,    11   b  of base  11 . The piezoelectric/electrostrictive device is constructed in a simple structure with fewer components. Base  11  is integrally formed in an open-box shape or in a horseshoe shape by bending one sheet of band-shaped flat plate. Movable parts  11   a,    11   b  extend for a predetermined length from respective ends of connecting part  11   c  to the other ends. The other ends of movable parts  11   a,    11   b  constitute a mounting site for mounting a component to be controlled or a component to be tested.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piezoelectric/electrostrictivedevice, a base constituting the piezoelectric/electrostrictive device,and a method of producing the piezoelectric/electrostrictive device.

2. Description of the Background Art

As one form of piezoelectric/electrostrictive device, there is known apiezoelectric/electrostrictive device of a form that includes a basehaving a pair of movable parts that are arranged in parallel with eachother to oppose each other and a connecting part that connects the twomovable parts with each other at one end thereof as well as apiezoelectric/electrostrictive element disposed on an outer side surfaceof at least one of the two movable parts of the base, as disclosed inthe specification of European Patent EP1017116A2.

The piezoelectric/electrostrictive device of such a form has a functionof operating the movable parts caused by the displacement operation ofthe piezoelectric/electrostrictive element or a sensing function ofsensing the displacement of the movable parts input from the side thatis sensed, with the use of the piezoelectric/electrostrictive element.By effectively using these functions, the piezoelectric/electrostrictivedevice is used in a wide range of fields such as described below.

Namely, the piezoelectric/electrostrictive devices of such a form areused as active elements such as various transducers, various actuators,frequency region functional components (filters), transformers,vibrators and resonators for communication or mechanical power,oscillators, and discriminators, various sensor elements such assupersonic wave sensors, acceleration sensors, angular velocity sensors,impact sensors, and mass sensors, and various actuators that are put touse for displacement, positioning adjustment, and angle adjustmentmechanism for various precision components of optical instruments andprecision apparatus.

Meanwhile, the piezoelectric/electrostrictive device of such a form isgenerally composed of a base and at least onepiezoelectric/electrostrictive element, and these are bonded to eachother via an adhesive. Further, the base is composed of constructionmembers that constitute a pair of movable parts and another constructionmember that connects these two construction members, and theseconstruction members are bonded to each other via an adhesive.

Thus, the piezoelectric/electrostrictive device having such a form has alarge number of construction members, so that the device is produced ata high cost and through a troublesome assembling work. Moreover, sincethe construction members are bonded to each other via an adhesive, therearises a dispersion of adhesion between the construction members, givingrise to a fear that the device characteristics may be adverselyaffected.

Further, the piezoelectric/electrostrictive device having such a form isproduced by adopting means for cutting a device master suitably into alarge number of devices. Therefore, the piezoelectric/electrostrictivedevices formed by cutting are contaminated with dusts generated at theprocess of cutting, cutting fluid, and organic components such as anadhesive or wax used for holding the device master at the process ofcutting, so that it is not easy to clean thepiezoelectric/electrostrictive device.

Further, in the case where the base is constructed with a ceramic, i.e.a sintered body formed from plural sheets of ceramic green sheetlaminates, one must adopt a hard ceramic material such as zirconia,since the ceramics are liable to be split. Even if a hard ceramicmaterial is adopted, one must choose a suitable cutting condition so asnot to generate loss of the material or cracks. Furthermore, since thebase is made of a hard ceramic material, the machining process isdifficult and, in order to increase process capacity, one must give acareful consideration such as use of a large number of machiningapparatus having different functions.

Here, the base can be constructed with a metal material; however, themetal material gives rise to an oxidized end surface by friction heatduring the cutting process and burrs remain on the processed endsurface, so that one must add another step of removing these. Further,the piezoelectric/electrostrictive device can be tested only after thedevice master is cut.

Further, the device cut out from the device master is preferably cleanedby adopting supersonic wave cleaning so that the contamination can beeasily removed. However, if a strong supersonic wave is used to obtain ahigh cleaning effect in supersonic wave cleaning, the device may bedamaged, and the piezoelectric/electrostrictive element may be broken orexfoliated from the base. For this reason, if the supersonic wavecleaning is adopted, one must select a weak supersonic wave that doesnot give damages to the device. However, if such a cleaning condition isadopted, a long period of time is needed in removing the contaminationthat has adhered at the process of cutting.

Dust generation from the piezoelectric/electrostrictive device may causethe following problems. For example, in the case where thepiezoelectric/electrostrictive device is used as an actuator of amagnetic head in a hard disk drive, if dust is generated in the drive,the dust may cause crash of the floating slider onto the medium, therebyraising a fear of data destruction. Also, for thepiezoelectric/electrostrictive device itself, the dust may adhere to theelectrode of the piezoelectric/electrostrictive device, thereby givingrise to a fear of short circuit. For this reason, a high level ofcleaning is required not only in the hard disk drive but also in thedevice itself.

Therefore, an object of the present invention is to solve theaforementioned problems of the prior art by allowing the baseconstituting the piezoelectric/electrostrictive device of that form tohave an integral structure using one sheet of flat plate as an originalplate.

SUMMARY OF THE INVENTION

The present invention relates to a piezoelectric/electrostrictive deviceand is directed to a piezoelectric/electrostrictive device of a formthat includes a base having a pair of movable parts that are arranged inparallel with each other to oppose each other and a connecting part thatconnects the two movable parts with each other at one end thereof aswell as a piezoelectric/electrostrictive element disposed on an outerside surface of at least one of the two movable parts of the base.

Here, the piezoelectric/electrostrictive device according to the presentinvention is constructed in such a manner that the base constituting thepiezoelectric/electrostrictive device of the above-described form isintegrally constructed with one sheet of band-shaped flat plate, and themovable parts extend for a predetermined length from respective ends ofthe aforesaid connecting part to other ends.

In the aforesaid piezoelectric/electrostrictive device, the base can beconstructed with a flat plate made of metal. Further, the aforesaidpiezoelectric/electrostrictive device can be used in a mode in which acomponent to be controlled or tested is sandwiched between innersurfaces of the other ends of the two movable parts constituting thebase.

The piezoelectric/electrostrictive device according to the presentinvention can be constructed in such a manner that thepiezoelectric/electrostrictive element is shorter than the movable partsand is positioned either at the other end of the movable parts or at theone end of the movable parts.

The piezoelectric/electrostrictive device according to the presentinvention can be constructed in such a manner that the base has agenerally open-box shape that is open to the other end of the twomovable parts. In this case, the piezoelectric/electrostrictive devicecan be constructed in such a manner that the base includes a flat platepart disposed on an inner surface or on an outer surface of theconnecting part. Further, the piezoelectric/electrostrictive deviceaccording to the present invention can be constructed in such a mannerthat the base has a generally horseshoe shape that is open to the otherend of the two movable parts, or in such a manner that the connectingsites between the ends of the connecting part and the movable parts areformed as recesses having a circular arc shape. Furthermore, thepiezoelectric/electrostrictive device according to the present inventioncan be constructed in such a manner that the movable parts of the baseinclude thinned portions located in a middle of a length thereof.

The present invention also provides a method of producing a baseconstituting a piezoelectric/electrostrictive device according to thepresent invention, including the steps of preparing a flexible andbendable flat plate as a material for forming the base; cutting the flatplate into flat plates each having a shape that delineates a planardevelopment of the base thereby to form original plates having a narrowstrip shape; and bending each of the original plates at predeterminedsites to form the base integrally having the two movable parts and theconnecting part.

Further, the present invention provides a method of producing apiezoelectric/electrostrictive device according to the presentinvention, including the steps of preparing a flexible and bendable flatplate as a material for forming the base; cutting the flat plate intoflat plates each having a shape that delineates a planar development ofthe base thereby to form original plates having a narrow strip shape;bending each of the original plates at predetermined sites so as to formthe base integrally having the two movable parts and the connectingpart; and bonding a piezoelectric/electrostrictive element onto an outerside surface of at least one of the two movable parts constituting thebase thereby to form the piezoelectric/electrostrictive device.

Furthermore, another method of producing apiezoelectric/electrostrictive device according to the present inventionincludes the steps of preparing a flexible and bendable flat plate as amaterial for forming the base, the flat plate having apiezoelectric/electrostrictive element bonded thereto at a predeterminedsite in advance; cutting the flat plate integrally with thepiezoelectric/electrostrictive element into flat plates each having ashape that delineates a planar development of the base thereby to formoriginal plates having a narrow strip shape; and bending each of theoriginal plates at predetermined sites to form the base integrallyhaving the two movable parts and the connecting part and to form thepiezoelectric/electrostrictive device having thepiezoelectric/electrostrictive element bonded onto an outer side surfaceof at least one of the two movable parts.

The piezoelectric/electrostrictive device according to the presentinvention has an integral structure in which the base constituting thepiezoelectric/electrostrictive device is constructed with one sheet ofband-shaped flat plate, so that the base is in principle constructedwith one piece of construction member. Therefore, the constructionmembers of each device are two kinds, namely, the base and thepiezoelectric/electrostrictive element, so that the number ofconstruction members of the piezoelectric/electrostrictive device can begreatly reduced, and man hour for assembling the construction memberscan be greatly reduced, thereby leading to large reduction of costs.

Further, in the piezoelectric/electrostrictive device according to thepresent invention, since the number of construction members is extremelysmall and the number of bonding sites between the construction membersis extremely small, there is little or no dispersion in the adhesionbetween the construction members, whereby thepiezoelectric/electrostrictive device has device characteristics inwhich the set precision is high.

Such an effective piezoelectric/electrostrictive device can be producedwith ease and at a low cost by each of the above-described productionmethods according to the present invention. In particular, the baseconstituting the piezoelectric/electrostrictive device according to thepresent invention can be produced with ease and at a low cost byadopting a production method including the steps of preparing a flexibleand bendable flat plate as a material for forming the base; cutting theflat plate into flat plates each having a shape that delineates a planardevelopment of the base thereby to form original plates having a narrowstrip shape; and bending each of the original plates at predeterminedsites to form the base integrally having the two movable parts and theconnecting part.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features, aspects, and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings, in which,

FIGS. 1A to 1H are perspective model views respectively illustratingeight types of embodiments of the piezoelectric/electrostrictive devicesaccording to the present invention;

FIG. 2A is a perspective view illustrating a method of preparing a flatplate for forming an original plate that constitutes a base of the firstpiezoelectric/electrostrictive device which is the first embodiment ofthe present invention; and FIG. 2B is a perspective view of the flatplate;

FIG. 3A is a perspective view illustrating a method of preparing theoriginal plate of the base that constitutes the firstpiezoelectric/electrostrictive device; FIG. 3B is a perspective view ofthe original plate; and FIG. 3C is a perspective view of thepiezoelectric/electrostrictive device composed of the base that isformed from the original plate;

FIG. 4A is a perspective view illustrating a method of preparing theoriginal plate of the base that constitutes the secondpiezoelectric/electrostrictive device; FIG. 4B is a perspective view ofthe original plate; and FIG. 4C is a perspective view of thepiezoelectric/electrostrictive device composed of the base that isformed from the original plate;

FIG. 5A is a perspective view illustrating a method of preparing theoriginal plate of the base that constitutes the thirdpiezoelectric/electrostrictive device; FIG. 5B is a perspective view ofthe original plate; and FIG. 5C is a perspective view of thepiezoelectric/electrostrictive device composed of the base that isformed from the original plate;

FIG. 6A is a perspective view illustrating a method of preparing theoriginal plate of the base that constitutes the fourthpiezoelectric/electrostrictive device; FIG. 6B is a perspective view ofthe original plate; and FIG. 6C is a perspective view of thepiezoelectric/electrostrictive device composed of the base that isformed from the original plate;

FIG. 7A is a perspective view illustrating a method of preparing theoriginal plate of the base that constitutes the fifthpiezoelectric/electrostrictive device; FIG. 7B is a perspective view ofthe original plate; and FIG. 7C is a perspective view of thepiezoelectric/electrostrictive device composed of the base that isformed from the original plate;

FIG. 8A is a perspective view illustrating a method of preparing theoriginal plate of the base that constitutes the sixthpiezoelectric/electrostrictive device; FIG. 8B is a perspective view ofthe original plate; and FIG. 8C is a perspective view of thepiezoelectric/electrostrictive device composed of the base that isformed from the original plate;

FIG. 9A is a perspective view illustrating a method of preparing theoriginal plate of the base that constitutes the seventhpiezoelectric/electrostrictive device; FIG. 9B is a perspective view ofthe original plate; and FIG. 9C is a perspective view of thepiezoelectric/electrostrictive device composed of the base that isformed from the original plate;

FIG. 10A is a perspective view illustrating a method of preparing theoriginal plate of the base that constitutes the eighthpiezoelectric/electrostrictive device; FIG. 10B is a perspective view ofthe original plate; and FIG. 10C is a perspective view of thepiezoelectric/electrostrictive device composed of the base that isformed from the original plate;

FIGS. 11A and 11B are perspective views illustrating two examples ofpiezoelectric/electrostrictive elements adopted as thepiezoelectric/electrostrictive element constituting thepiezoelectric/electrostrictive device according to the presentinvention;

FIG. 12A and FIG. 12B are perspective views illustrating two otherexamples of piezoelectric/electrostrictive elements adopted as thepiezoelectric/electrostrictive element constituting thepiezoelectric/electrostrictive device according to the presentinvention;

FIG. 13 is a plan view of a piezoelectric/electrostrictive deviceaccording to an example of the present invention which is formed byadopting the piezoelectric/electrostrictive element shown in FIG. 12B asthe piezoelectric/electrostrictive element;

FIG. 14 is a plan view of the piezoelectric/electrostrictive device inan operating state;

FIGS. 15A and 15B are waveform diagrams respectively showing voltagesapplied to the two piezoelectric/electrostrictive elements of thepiezoelectric/electrostrictive device;

FIG. 16 is a schematic perspective view illustrating an embodiment inwhich the piezoelectric/electrostrictive device is used as anacceleration sensor; and

FIG. 17 is a perspective view illustrating the acceleration sensor in astate before assembling.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a piezoelectric/electrostrictive device thatincludes a base having a pair of movable parts that are arranged inparallel with each other to oppose each other and a connecting part thatconnects the two movable parts with each other at one end thereof aswell as a piezoelectric/electrostrictive element disposed on an outerside surface of at least one of the two movable parts in the base,wherein the base is integrally formed with one sheet of band-shaped flatplate that is bent in an open-box shape or in a horseshoe shape. FIGS.1A to 1H are model views respectively illustrating numerous embodiments(first embodiment to eighth embodiment) of thepiezoelectric/electrostrictive devices according to the presentinvention.

The first to sixth embodiments shown in FIGS. 1A to 1F arepiezoelectric/electrostrictive devices in which the base has an open-boxshape. The seventh embodiment shown in FIG. 1G is apiezoelectric/electrostrictive device in which the base has a horseshoeshape. The eighth embodiment shown in FIG. 1H is apiezoelectric/electrostrictive device in which the base has an open-boxshape, and the connecting sites between the ends of the connecting partand the movable part's are formed as recesses having a circular arcshape.

The first piezoelectric/electrostrictive device 10 a constituting thefirst embodiment and the second piezoelectric/electrostrictive device 10b constituting the second embodiment have a basic construction of thepiezoelectric/electrostrictive device according to the presentinvention. The first piezoelectric/electrostrictive device 10 a isformed by the method shown in FIGS. 2 and 3, and the secondpiezoelectric/electrostrictive device 10 b is formed by the method shownin FIG. 4.

Referring to FIG. 3C, the first piezoelectric/electrostrictive device 10a is made of a base 11 and a pair of piezoelectric/electrostrictiveelements 12 a, 12 b. Base 11 is formed by bending a long and narroworiginal plate into an open-box shape, and is constructed with a pair ofright and left movable parts 11 a, 11 b and a connecting part 11 c thatconnects the two movable parts 11 a, 11 b with each other at one endthereof. In the base 11, the piezoelectric/electrostrictive elements 12a, 12 b are bonded respectively to outer side surfaces of the movableparts 11 a, 11 b via an adhesive made of epoxy resin or the like.

Each of Piezoelectric/electrostrictive elements 12 a, 12 b is a laminatebody made of piezoelectric/electrostrictive layers and electrode films,and is formed to have the same shape as movable parts 11 a, 11 b and tobe shorter by a predetermined length than movable parts 11 a, 11 b.Piezoelectric/electrostrictive elements 12 a, 12 b are bonded at one endof movable parts 11 a, 11 b in proximity to connecting part 11 c andextend for a predetermined length towards the other end of movable parts1 a, 11 b.

The first piezoelectric/electrostrictive device 10 a is used in such amanner that an actuator (not illustrated) is disposed on connecting part11 c of base 11, and a magnetic head (slider) for a hard disk, which isa component to be controlled (not illustrated), for example, is disposedbetween the two movable parts 11 a, 11 b.

Now, as the original plate for constructing the base 11 constituting thefirst piezoelectric/electrostrictive device 10 a, an original plate 11Aillustrated in FIG. 3B is adopted, and the original plate 11A is formedby the method shown in FIGS. 2A, 2B, and 3A. The original plate 11Aillustrated in FIG. 3B is formed into the firstpiezoelectric/electrostrictive device 10 a illustrated in FIG. 3C bybending the original plate 11A along two-dot chain lines shown in FIG.3B.

The original plate 11A is basically made of a flat plate 11A1 shown inFIGS. 2A and 2B; further, two sheets of longpiezoelectric/electrostrictive element master plates 12A, 12B, whichwill later become piezoelectric/electrostrictive elements 12 a, 12 b,are bonded thereto. Flat plate 11 a 1 having twopiezoelectric/electrostrictive element master plates 12A, 12B bondedthereto is cut at numerous sites along the one-dot chain lines shown inFIG. 3A and lines parallel thereto, whereby numerous original plates 11Ashown in FIG. 3B are formed. Original plate 11A is bent along thetwo-dot chain lines shown in FIG. 3B to form the firstpiezoelectric/electrostrictive device 10 a shown in FIG. 3C.

Flat plate 11 a 1 is preferably a flat plate that is flexible and madeof a metal having Young's modulus of 100 GPa or higher. As aniron-series material satisfying these properties, one can mentionaustenite-series stainless steels such as SUS301, SUS304, AISI653, andSUH660, ferrite-series stainless steels such as SUS430 and SUS434,martensite-series stainless steels such as SUS410 and SUS630,semiaustenite-series stainless steels such as SUS6312 and AISI632,maraging stainless steel, and steel materials such as various springsteels. As a non-iron-series material, one can mention superelastictitanium alloys such as a titanium-nickel alloy, brass, cupronickel,aluminum, tungsten, molybdenum, beryllium copper, phosphorus bronze,nickel, a nickel iron alloy, titanium, and others.

Here, in constructing the base with a metal material, it is preferableto adopt a metal plate in which at least the sites corresponding to themovable parts of the base are cold-rolled.

Thus, the first piezoelectric/electrostrictive device 10 a functions inthe same manner as the conventional piezoelectric/electrostrictivedevices of this form and, since base 11 has an integral structure havingoriginal plate 11A as a construction member,piezoelectric/electrostrictive device 10 a produces the followingfunctions and effects.

Namely, the first piezoelectric/electrostrictive device 10 a isconstructed with base 11 having an integral structure made of originalplate 11A alone. Therefore, the construction members are two kinds,namely, base 11 and piezoelectric/electrostrictive elements (12 a, 12b), so that the number of construction members ofpiezoelectric/electrostrictive device 10 a can be greatly reduced, andman hour for assembling the construction members can be greatly reduced,thereby leading to large reduction of costs.

Further, in the first piezoelectric/electrostrictive device 1 a, sincethe number of construction members is extremely small and the number ofbonding sites between the construction members is extremely small, thereis little or no dispersion in the adhesion between the constructionmembers, whereby the piezoelectric/electrostrictive device has devicecharacteristics in which the set precision is high.

Furthermore, the first piezoelectric/electrostrictive device 10 a has aconstruction such that original plate 11A is formed by bondingpiezoelectric/electrostrictive element master plates 12A, 12B in advanceonto the material (flat plate 11 a 1) for forming original plate 11A,which is a construction member of base 11, and cutting flat plate 11 a 1integrally with piezoelectric/electrostrictive element master plates12A, 12B. Therefore, in assembling the piezoelectric/electrostrictivedevice, the work of bonding piezoelectric/electrostrictive elements 12a, 12 b onto movable parts 1 a, 11 b, which are extremely narrow andfine sites, can be eliminated, so that the assembling work is easy, andthe precision of bonding piezoelectric/electrostrictive elements 12 a,12 b onto movable parts 11 a, 11 b can be further improved.

The second piezoelectric/electrostrictive device 10 b shown in FIG. 1Band constituting the second embodiment of the present invention hasanother basic construction of the piezoelectric/electrostrictive deviceaccording to the present invention and is formed by the method shown inFIG. 4.

Referring to FIG. 4C, the second piezoelectric/electrostrictive device10 b is made of a base 13 and a pair of piezoelectric/electrostrictiveelements 12 a, 12 b. On this point, the secondpiezoelectric/electrostrictive device 10 b is the same as the firstpiezoelectric/electrostrictive device 10 a; however, the secondpiezoelectric/electrostrictive device 10 b is different from the firstpiezoelectric/electrostrictive device 10 a only in the position ofdisposing the piezoelectric/electrostrictive elements 12 a, 12 b. In thesecond piezoelectric/electrostrictive device 10 b,piezoelectric/electrostrictive elements 12 a, 12 b are bonded to theother end of movable parts 13 a, 13 b, and extend for a predeterminedlength towards the one end of movable parts 11 a, 11 b, namely, towardsthe connecting part 13 c side of base 13.

Now, as the original plate for constructing base 13 that constitutes thesecond piezoelectric/electrostrictive device 10 b, an original plate 13Ashown in FIG. 4B is adopted, and original plate 13A is formed by cuttinga flat plate 13A1 shown in FIG. 4A along one-dot chain lines.Piezoelectric/electrostrictive element master plates 12A, 12B are bondedto end peripheries (as viewed in the forward-and-backward direction) offlat plate 13A1, and flat plate 13A1 is cut not only along the one-dotchain lines at two sites but also along numerous cutting lines (notillustrated) parallel to these one-dot chain lines, whereby numerousoriginal plates 13A are cut out.

Original plate 13A is bent along the two-dot chain lines shown in FIG.4B to be formed into the second piezoelectric/electrostrictive device 10b shown in FIG. 4C. The second piezoelectric/electrostrictive device 10b is different in construction from the firstpiezoelectric/electrostrictive device 10 a in that the twopiezoelectric/electrostrictive elements 12 a, 12 b are placed at theother end of the two movable parts 13 a, 13 b; however, the two have thesame construction on the other points. Therefore, the secondpiezoelectric/electrostrictive device 10 b has a function similar tothat of the first piezoelectric/electrostrictive device 10 a, andproduces similar actions and effects.

The third and fourth piezoelectric/electrostrictive devices 10 c, 10 dshown in FIGS. 1C and 1D and constituting the third and fourthembodiments of the present invention are based on the firstpiezoelectric/electrostrictive device 10 a in construction. The fifthand sixth piezoelectric/electrostrictive devices 10 e, 10 f shown inFIGS. 1E and 1F and constituting the fifth and sixth embodiments of thepresent invention are based on the second piezoelectric/electrostrictivedevice 10 b in construction.

Referring to FIG. 5C, the third piezoelectric/electrostrictive device 10c shown in FIG. 1C is made of a base 14 and a pair ofpiezoelectric/electrostrictive elements 12 a, 12 b. On this point, thethird piezoelectric/electrostrictive device 10 c is the same as thefirst piezoelectric/electrostrictive device 10 a; however, the thirdpiezoelectric/electrostrictive device 10 c is different from the firstpiezoelectric/electrostrictive device 10 a in that a flat plate part 14d is disposed on the connecting part 14 c constituting the base 14. Flatplate part 14 d is placed on the inner surface side of connecting part14 c between the two movable parts 14 a, 14 b. Flat plate part 14 dfunctions to reinforce connecting part 14 c, and also functions toenlarge the bonding area to an actuator or the like when connecting part14 c is used as a supporting part for the actuator or the like.

Now, as the original plate for constructing base 14 of the thirdpiezoelectric/electrostrictive device 10 c, an original plate 14A shownin FIG. 5B is adopted, and original plate 14A is formed by cutting aflat plate 14A1 shown in FIG. 5A along one-dot chain lines.Piezoelectric/electrostrictive element master plates 12A, 12B are bondedto two sites in the middle part (as viewed in the forward-and-backwarddirection) on the front surface of flat plate 14A1, and aflat-plate-shaped member 14D that forms flat plate part 14 d is bondedto the central part (as viewed in the forward-and-backward direction) onthe rear surface of flat plate 14A1. Flat plate 14A1 is cut along theone-dot chain lines shown in FIG. 5A and along cutting lines (notillustrated) parallel to these one-dot chain lines, whereby numerousoriginal plates 14A are cut out.

Original plate 14A is bent along the two-dot chain lines shown in FIG.5B to be formed into the third piezoelectric/electrostrictive device 10c shown in FIG. 5C. The third piezoelectric/electrostrictive device 10 cis different in construction from the firstpiezoelectric/electrostrictive device 10 a in that the thirdpiezoelectric/electrostrictive device 10 c includes flat plate part 14d; however, the two have the same construction on the other points.Therefore, the third piezoelectric/electrostrictive device 10 c has afunction similar to that of the first piezoelectric/electrostrictivedevice 10 a, and produces similar actions and effects. However, due toflat plate part 14 d, the third piezoelectric/electrostrictive device 10c has a function of reinforcing connecting part 14 c and a function ofenlarging the bonding area to connecting part 14 c.

Referring to FIG. 6C, the fourth piezoelectric/electrostrictive device10 d shown in FIG. 1D is made of a base 15 and a pair ofpiezoelectric/electrostrictive elements 12 a, 12 b. On this point, thefourth piezoelectric/electrostrictive device 10 d is the same as thefirst piezoelectric/electrostrictive device 10 a; however, the fourthpiezoelectric/electrostrictive device 10 d is different from the firstpiezoelectric/electrostrictive device 10 a in that a flat plate part 15d is disposed on the connecting part 15 c constituting the base 15. Flatplate part 15 d is placed on the outer surface side of connecting part15 c, that is, on the side opposite to the space between the two movableparts 15 a, 15 b. Flat plate part 15 d functions to enlarge the bondingarea to an actuator or the like when connecting part 15 c is used as asupporting part for the actuator or the like.

Now, as the original plate for constructing base 15 of the fourthpiezoelectric/electrostrictive device 10 d, an original plate 15A shownin FIG. 6B is adopted, and original plate 15A is formed by cutting aflat plate 15A1 shown in FIG. 6A along one-dot chain lines.Piezoelectric/electrostrictive element master plates 12A, 12B are bondedto two sites in the middle part (as viewed in the forward-and-backwarddirection) on the front surface of flat plate 15A1, and aflat-plate-shaped member 15D that forms flat plate part 15 d is bondedto the central part (as viewed in the forward-and-backward direction) onthe front surface of flat plate 15A1. Flat plate 15A1 is cut along theone-dot chain lines shown in FIG. 6A and along cutting lines (notillustrated) parallel to these one-dot chain lines, whereby numerousoriginal plates 15A are cut out.

Original plate 15A is bent along the two-dot chain lines shown in FIG.6B to be formed into the fourth piezoelectric/electrostrictive device 10d shown in FIG. 6C. The fourth piezoelectric/electrostrictive device 10d is different in construction from the firstpiezoelectric/electrostrictive device 10 a in that the fourthpiezoelectric/electrostrictive device 10 d includes flat plate part 15d; however, the two have the same construction on the other points.Therefore, the fourth piezoelectric/electrostrictive device 10 d has afunction similar to that of the first piezoelectric/electrostrictivedevice 10 a, and produces similar actions and effects. However, due toflat plate part 15 d, the fourth piezoelectric/electrostrictive device10 d exhibits a function of enlarging the bonding area to connectingpart 15 c.

The fifth piezoelectric/electrostrictive devices 10 e shown in FIG. 1Eis based on the second piezoelectric/electrostrictive device 10 b shownin FIG. 1B in construction. Referring to FIG. 7C, the fifthpiezoelectric/electrostrictive device 10 e shown in FIG. 1E is made of abase 16 and a pair of piezoelectric/electrostrictive elements 12 a, 12b. On this point, the fifth piezoelectric/electrostrictive device 10 eis the same as the second piezoelectric/electrostrictive device 10 b;however, the fifth piezoelectric/electrostrictive device 10 e isdifferent from the second piezoelectric/electrostrictive device 10 b inthat a flat plate part 16 d is disposed on the connecting part 16 cconstituting the base 16. Flat plate part 16 d is placed on the outersurface side of connecting part 16 c, that is, on the side opposite tothe space between the two movable parts 16 a, 16 b. Flat plate part 16 dfunctions to enlarge the bonding area to an actuator or the like whenconnecting part 16 c is used as a supporting part for the actuator orthe like.

Now, as the original plate for constructing base 16 of the fifthpiezoelectric/electrostrictive device 10 e, an original plate 16A shownin FIG. 7B is adopted, and original plate 16A is formed by cutting aflat plate 16A1 shown in FIG. 7A along one-dot chain lines.Piezoelectric/electrostrictive element master plates 12A, 12B are bondedto two end sites (as viewed in the forward-and-backward direction) onthe front surface of flat plate 16A1, and a flat-plate-shaped member 16Dthat forms flat plate part 16 d is bonded to the central part (as viewedin the forward-and-backward direction) on the front surface of flatplate 16A1. Flat plate 16A1 is cut along the one-dot chain lines shownin FIG. 7A and along cutting lines (not illustrated) parallel to theseone-dot chain lines, whereby numerous original plates 16A are cut out.

Original plate 16A is bent along the two-dot chain lines shown in FIG.7B to be formed into the fifth piezoelectric/electrostrictive device 10e shown in FIG. 7C. The fifth piezoelectric/electrostrictive device 10 eis different in construction from the secondpiezoelectric/electrostrictive device 10 b in that the fifthpiezoelectric/electrostrictive device 10 e includes flat plate part 16d; however, the two have the same construction on the other points.Therefore, the fifth piezoelectric/electrostrictive device 10 e has afunction similar to that of the second piezoelectric/electrostrictivedevice 10 b, and produces similar actions and effects. However, due toflat plate part 16 d, the fifth piezoelectric/electrostrictive device 10e exhibits a function of enlarging the bonding area to connecting part16 c.

The sixth piezoelectric/electrostrictive device 10 f shown in FIG. 1F isbased on the second piezoelectric/electrostrictive device 10 b shown inFIG. 1B in construction, and has the same construction as the fifthpiezoelectric/electrostrictive device 10 e in that the sixthpiezoelectric/electrostrictive device 10 f is made of a base 17 and apair of piezoelectric/electrostrictive elements 12 a, 12 b and in that aflat plate part 17 d is disposed on the connecting part 17 cconstituting the base 17, as illustrated in FIG. 8C. However, the sixthpiezoelectric/electrostrictive device 10 f is different from the fifthpiezoelectric/electrostrictive device 10 e in that middle parts (asviewed in the longitudinal direction) of the two movable parts 17 a, 17b are formed into thinned parts 17 a 1, 17 b 1 for a predeterminedlength. Thinned parts 17 a 1, 17 b 1 of the two movable parts 17 a, 17 bfunction to increase the amount of displacement of the two movable parts17 a, 17 b.

Now, as the original plate for constructing base 17 of the sixthpiezoelectric/electrostrictive device 10 f, an original plate 17A shownin FIG. 8B is adopted, and original plate 17A is formed by cutting aflat plate 17A1 shown in FIG. 8A along one-dot chain lines.Piezoelectric/electrostrictive element master plates 12A, 12B are bondedto two end sites (as viewed in the forward-and-backward direction) onthe front surface of flat plate 17A1, and a flat-plate-shaped member 17Dthat forms flat plate part 17 d is bonded to the central part (as viewedin the forward-and-backward direction) on the front surface of flatplate 17A1.

In flat plate 17A1, two sites in the middle part (as viewed in theforward-and-backward direction) of flat plate 17A1 are formed intothinned parts 17 a 1, 17 b 1 for a predetermined length. Flat plate 17A1is cut along the one-dot chain lines shown in FIG. 8A and along cuttinglines (not illustrated) parallel to these one-dot chain lines, wherebynumerous original plates 17A are cut out.

Original plate 17A is bent along the two-dot chain lines shown in FIG.8B to be formed into the sixth piezoelectric/electrostrictive device 10f shown in FIG. 8C. The sixth piezoelectric/electrostrictive device 10 fis different in construction from the fifthpiezoelectric/electrostrictive device 10 e in that movable parts 17 a,17 b include thinned parts 17 a 1, 17 b 1; however, the two have thesame construction on the other points. Therefore, the sixthpiezoelectric/electrostrictive device 10 f has a function similar tothat of the fifth piezoelectric/electrostrictive device 10 e, andproduces similar actions and effects. However, due to thinned parts 17 a1, 17 b 1, the sixth piezoelectric/electrostrictive device 10 f exhibitsa function of increasing the amount of displacement of movable parts 17a, 17 b.

Here, thinned parts 17 a 1, 17 b 1 of flat plate 17A1 and movable parts17 a, 17 b in base 17 can be formed by adopting means such as etching,laser machining, electric discharge machining, ion milling, sandblasting, or drill machining. Alternatively, thinned parts 17 a 1, 17 b1 can be formed by preparing extra plates that have been subjected tostamping, and laminating and bonding the plates onto the correspondingsites on a base plate.

The seventh piezoelectric/electrostrictive device 10 g and the eighthpiezoelectric/electrostrictive device 10 h shown in FIGS. 1G and 1H andconstituting the seventh and eighth embodiments of the present inventionare different in form from the first piezoelectric/electrostrictivedevice b1 a and the second piezoelectric/electrostrictive device 10 bconstituting the first and second embodiments of the present invention.

Referring to FIG. 9C, the seventh piezoelectric/electrostrictive device10 g constituting the seventh embodiment of the present invention ismade of a base 18 and a pair of piezoelectric/electrostrictive elements12 a, 12 b, and is different from the secondpiezoelectric/electrostrictive device 10 b in that the connecting part18 c constituting the base 18 has a circular arc shape. Connecting part18 c having a circular arc shape functions to achieve an increase in theamount of displacement and a smooth displacement operation of the twomovable parts 18 a, 18 b.

Now, as the original plate for constructing base 18 of the seventhpiezoelectric/electrostrictive device 10 g, an original plate 18A shownin FIG. 9B is adopted, and original plate 18A is formed by cutting aflat plate 18A1 shown in FIG. 9A along one-dot chain lines.Piezoelectric/electrostrictive element master plates 12A, 12B are bondedto two end sites (as viewed in the forward-and-backward direction) onthe front surface of flat plate 18A1. Flat plate 18A1 is cut along theone-dot chain lines shown in FIG. 9A and along cutting lines (notillustrated) parallel to these one-dot chain lines, whereby numerousoriginal plates 18A are cut out.

Original plate 18A is bent along the two-dot chain lines shown in FIG.9B to be formed into the seventh piezoelectric/electrostrictive device10 g shown in FIG. 9C. The seventh piezoelectric/electrostrictive device10 g is different in construction from the secondpiezoelectric/electrostrictive device 10 b in that the connecting part18 c that connects the two movable parts 18 a, 18 b exhibits a circulararc shape; however, the two have the same construction on the otherpoints. Therefore, the seventh piezoelectric/electrostrictive device 10g has a function similar to that of the secondpiezoelectric/electrostrictive device 10 b, and produces similar actionsand effects. However, due to connecting part 18 c having a circular arcshape, the seventh piezoelectric/electrostrictive device 10 g functionsto achieve an increase in the amount of displacement and a smoothdisplacement operation of the two movable parts 18 a, 18 b.

Referring to FIG. 10C, the eighth piezoelectric/electrostrictive device10 h shown in FIG. 1H is made of a base 19 and a pair ofpiezoelectric/electrostrictive elements 12 a, 12 b, and is differentfrom the second piezoelectric/electrostrictive device 10 b in that theconnecting sites 19 c 1, 19 c 2 that connect the connecting part 19 c tomovable parts 19 a, 19 b constituting the base 19 are formed as recesseshaving a circular arc shape. The recessed connecting sites 19 c 1, 19 c2 having a circular arc shape function to achieve an increase in theamount of displacement and a smooth displacement operation of the twomovable parts 19 a, 19 b.

Now, as the original plate for constructing base 19 of the eighthpiezoelectric/electrostrictive device 10 h, an original plate 19A shownin FIG. 10B is adopted, and original plate 19A is formed by cutting aflat plate 19A1 shown in FIG. 10A along one-dot chain lines. Two sitesin the middle part (as viewed in the forward-and-backward direction) offlat plate 19A1 are formed to have an undulated shape. These undulatedsites 19 c 3, 19 c 4 correspond to the connecting sites 19 c 1, 19 c 2so as to form the connecting sites 19 c 1, 19 c 2 when original plate19A is bent. Piezoelectric/electrostrictive element master plates 12A,12B are bonded to two end sites (as viewed in the forward-and-backwarddirection) on the front surface of flat plate 19A1. Flat plate 19A iscut along the one-dot chain lines shown in FIG. 10A and along cuttinglines (not illustrated) parallel to these one-dot chain lines, wherebynumerous original plates 19A are cut out.

Original plate 19A is bent along the two-dot chain lines shown in FIG.10B to be formed into the eighth piezoelectric/electrostrictive device10 h shown in FIG. 10C. The eighth piezoelectric/electrostrictive device10 h is different in construction from the secondpiezoelectric/electrostrictive device 10 b in that the connecting sites19 c 1, 19 c 2 that connect the connecting part 19 c to the two movableparts 19 a, 19 b are formed as recesses having a circular arc shape;however, the two have the same construction on the other points.Therefore, the eighth piezoelectric/electrostrictive device 10 h has afunction similar to that of the second piezoelectric/electrostrictivedevice 10 b, and produces similar actions and effects. However, due toconnecting sites 19 c 1, 19 c 2, the eighthpiezoelectric/electrostrictive device 10 h functions to achieve anincrease in the amount of displacement and a smooth displacementoperation of the two movable parts 19 a, 19 b.

In the above-described methods for producing thepiezoelectric/electrostrictive devices, as means for cutting flat plates11A1 to 19A1 to which the piezoelectric/electrostrictive element masterplates are laminated and bonded, one can adopt means such as mechanicalmachining such as dicing machining or wire saw machining, lasermachining using laser such as YAG laser or excimer laser, or electronbeam machining.

The piezoelectric/electrostrictive elements 12 a, 12 b constituting thepiezoelectric/electrostrictive devices 10 a to 10 h according to theabove-described embodiments are each provided with apiezoelectric/electrostrictive layer and a pair of electrodes forapplying an electric field thereto, and arepiezoelectric/electrostrictive elements of unimorph type, bimorph type,or the like. Among these piezoelectric/electrostrictive elements,piezoelectric/electrostrictive elements of unimorph type are excellentin the stability of the deriving displacement, and are also advantageousfor weight reduction, so that they are suitable as a constructioncomponent of piezoelectric/electrostrictive devices.

FIGS. 11 and 12 illustrate several examples ofpiezoelectric/electrostrictive elements 21 to 24 that are suitablyadopted as the piezoelectric/electrostrictive elements 12 a, 12 bconstituting the piezoelectric/electrostrictive devices b1 a to 10 h.

Piezoelectric/electrostrictive element 21 shown in FIG. 11A has amonolayer structure in which the piezoelectric/electrostrictive layerconsists of one layer, and is constructed with apiezoelectric/electrostrictive layer 21 a, a pair of first and secondelectrodes 21 b, 21 c, and a pair of terminals 21 d, 21 e.Piezoelectric/electrostrictive element 22 shown in FIG. 11B has atwo-layer structure in which the piezoelectric/electrostrictive layerconsists of two layers, and is constructed withpiezoelectric/electrostrictive layers 22 a (22 a 1, 22 a 2), a firstelectrode 22 b that intervenes between the twopiezoelectric/electrostrictive layers 22 a 1, 22 a 2, a second electrode22 c that surrounds the outer sides of the twopiezoelectric/electrostrictive layers 22 a 1, 22 a 2, and a pair ofterminals 22 d, 22 e.

Piezoelectric/electrostrictive elements 23, 24 shown in FIG. 12 eachhave a four-layer structure in which the piezoelectric/electrostrictivelayer consists of four layers. Piezoelectric/electrostrictive element 23shown in FIG. 12A is constructed with piezoelectric/electrostrictivelayers 23 a (23 a 1 to 23 a 4), first and second electrodes 23 b, 23 cthat intervene between and surround these piezoelectric/electrostrictivelayers 23 a 1 to 23 a 4, and a pair of terminals 23 d, 23 e.

The piezoelectric/electrostrictive element 24 shown in FIG. 12B isdifferent from the piezoelectric/electrostrictive element 23 in that theterminals are placed at different sites. Piezoelectric/electrostrictiveelement 24 is constructed with piezoelectric/electrostrictive layers 24a (24 a 1 to 24 a 2), first and second electrodes 24 b, 24 c thatintervene between and surround the two piezoelectric/electrostrictivelayers 24 a 1 to 24 a 2, and a pair of terminals 24 d, 24 e.

These piezoelectric/electrostrictive elements 21 to 24 are suitablyadopted as the piezoelectric/electrostrictive elements 12 a, 12 b of thepiezoelectric/electrostrictive devices 10 a to 10 h in accordance withthe intended usage of the piezoelectric/electrostrictive devices.

Though piezoelectric ceramic is used in thepiezoelectric/electrostrictive layers 21 a to 24 a constituting thepiezoelectric/electrostrictive elements 21 to 24, one can useelectrostrictive ceramic, ferroelectric ceramic, antiferroelectricceramic, or the like as well. However, if thepiezoelectric/electrostrictive device is to be used as means forpositioning the magnetic head of a hard disk drive or the like purpose,it is preferable to use a material whose striction (distortion)hysteresis is small because the linearity between the displacementamount of the mounting part for mounting the magnetic head and thedriving voltage or the output voltage is essential. It is preferable touse a material having a coercive electric field of at most 10 kV/mm.

As a material for forming the piezoelectric/electrostrictive layers 21 ato 24 a, one can specifically mention lead zirconate, lead titanate,magnesium lead niobate, zinc lead niobate, manganese lead niobate,antimony lead stannate, manganese lead tungstate, cobalt lead niobate,barium titanate, bismuth sodium titanate, potassium sodium niobate,strontium bismuth tantalate, and others, which are used either alone oras a suitable mixture thereof. Particularly, a material containing leadzirconate, lead titanate, or magnesium lead niobate as a majorcomponent, or a material containing bismuth sodium titanate as a majorcomponent is suitable.

The characteristics of the piezoelectric/electrostrictive layers 21 a to24 a can be adjusted by adding a suitable material to the materials forforming the piezoelectric/electrostrictive layers 21 a to 24 a. As amaterial to be added, one can mention oxides of lanthanum, calcium,strontium, molybdenum, tungsten, barium, niobium, zinc, nickel,manganese, cesium, cadmium, chromium, cobalt, antimony, iron, yttrium,tantalum, lithium, bismuth, tin, and others, or materials thateventually become these oxides, which are used either alone or as asuitable mixture thereof.

For example, by allowing lanthanum or strontium to be contained, in leadzirconate, lead titanate, magnesium lead niobate, or the likeconstituting the major component, there will be provided an advantagethat the coercive electric field or the piezoelectric property can beadjusted. Here, it is preferable to avoid addition of a material thateasily undergoes vitrification, such as silica. This is because amaterial such as silica that easily undergoes vitrification is liable toreact with the piezoelectric/electrostrictive layers at the time ofthermal treatment of the piezoelectric/electrostrictive layers, andchanges their composition to deteriorate the piezoelectric properties.

The electrodes 21 b, 21 c to 24 b, 24 c constituting thepiezoelectric/electrostrictive elements 21 to 24 are preferably made ofa metal material that is solid at room temperature and excellent inelectrical conductivity. As a metal material, one can mention metalssuch as aluminum, titanium, chromium, iron, cobalt, nickel, copper,zinc, niobium, molybdenum, ruthenium, palladium, rhodium, silver, tin,tantalum, tungsten, iridium, platinum, gold, or lead, which are used asa single metal or an alloy of these metals. Further, one can use acermet material obtained by dispersing ceramics made of the samematerials as or made of different materials from thepiezoelectric/electrostrictive layers into these metal materials.

Piezoelectric/electrostrictive elements 21 to 24 are preferably formedby integrally sintering the piezoelectric/electrostrictive layers 21 ato 24 a and the electrodes 21 b, 21 c to 24 b, 24 c, in a mutuallylaminated state. In this case, as the electrodes, it is preferable toadopt those made of a high-melting-point metal material such asplatinum, palladium, or an alloy of these, or an electrode made of acermet material which is a mixture of a high-melting-point metalmaterial and the materials for forming thepiezoelectric/electrostrictive layers or other ceramic materials. Thethickness of the electrodes preferably has a film shape as thin aspossible because the thickness becomes a factor that affects thedisplacement of the piezoelectric/electrostrictive elements. For thisreason, in order that the electrodes formed by being integrally bakedwith the piezoelectric/electrostrictive layers have a film shape as thinas possible, it is preferable to use the material for forming theelectrodes in a form of a metal paste, for example, a gold resinatepaste, platinum resinate paste, silver resinate paste, or the like.

The thickness of each of the piezoelectric/electrostrictive elements 21to 24 is preferably within a range from 40 μm to 180 μm ifpiezoelectric/electrostrictive elements 21 to 24 are to be used as thepiezoelectric/electrostrictive elements 12 a, 12 b of thepiezoelectric/electrostrictive device according to each embodiment. Ifthe thickness is below 40 μm, piezoelectric/electrostrictive elements 21to 24 are liable to be broken during the handling, whereas if thethickness exceeds 180 μm, the scale reduction of the device will bedifficult. Further, by allowing the piezoelectric/electrostrictiveelements to have a multi-layer structure such as in thepiezoelectric/electrostrictive elements 23, 24, one can increase theoutput of the piezoelectric/electrostrictive elements to enlarge thedisplacement of the device. Furthermore, by allowing thepiezoelectric/electrostrictive elements to have a multi-layer structure,the rigidity of the device will be improved, thereby advantageouslyraising the resonance frequency of the device to increase the speed ofthe displacement operation of the device.

Piezoelectric/electrostrictive elements 21 to 24 are prepared usingmeans for cutting an original plate of a large area, which is formed bylaminating and sintering the piezoelectric/electrostrictive layers andthe electrodes by printing or tape molding, out into a predetermineddimension in a large number with the use of a dicing machine, a slicer,a wire saw, or the like. Piezoelectric/electrostrictive elements 21 to24 are thinner and have a lower hardness than known ceramic bases, sothat the speed of cutting the original plate can be set to be high,whereby the original plates can be processed in a large mass and at ahigh speed.

Piezoelectric/electrostrictive elements 21 to 24 have a simpleplate-shaped structure and can be easily handled with. Also, the amountof adhering dust is small, and the dust can be easily removed. However,since the piezoelectric/electrostrictive elements 21 to 24 are mainlymade of a ceramic material, a suitable cleaning condition must be set insupersonic wave cleaning. In a piezoelectric/electrostrictive elementcut out from the original plate, it is preferable to perform a precisioncleaning treatment by US cleaning and then perform a heat treatment at100° C. to 1000° C. in atmospheric air so as to completely remove themoisture and organic substances that have penetrated into the fine poresof the ceramic material.

To put the above-described productions of piezoelectric/electrostrictiveelements 21 to 24 together, for producing piezoelectric/electrostrictiveelements, one can use a thick film forming method such as the screenprinting method, the dipping method, the coating method, or theelectrophoresis method, or a thin film forming method such as the ionbeam method, the sputtering method, the vacuum vapor deposition method,the ion plating method, the chemical vapor deposition method (CVD), orthe plating method. In order to form piezoelectric/electrostrictiveelements by adopting these production methods, one can form apiezoelectric/electrostrictive element directly on a base or on a flatplate which is an original plate of the base. Alternatively, one mayform a piezoelectric/electrostrictive element on a suitable supportingsubstrate, and then peel the piezoelectric/electrostrictive element offfor bonding it onto a base or a flat plate.

If the piezoelectric/electrostrictive elements 21 to 24 are to beadopted as the piezoelectric/electrostrictive elements 12 a, 12 bconstituting the piezoelectric/electrostrictive devices 10 a to 10 haccording to each embodiment; it is preferable to use a resin-seriesadhesive such as epoxy resin, UV resin, or hot-melt adhesive, or aninorganic adhesive such as glass, cement, solder, or brazing material asa bonding means to the base of each of thepiezoelectric/electrostrictive elements 21 to 24. Also, a mixture ofresin-series adhesive with metal powder or ceramic powder can be used aswell. The hardness of the adhesive is preferably not less than 80 interms of Shore hardness D.

Further, as another mode for adopting the piezoelectric/electrostrictiveelements 21 to 24, one can adopt a mode in which apiezoelectric/electrostrictive element master plate similar topiezoelectric/electrostrictive element master plates 12A, 12B is bondedin advance onto a flat plate constituting the original plate of thebase, and this flat plate is cut at a suitable width to cut thepiezoelectric/electrostrictive elements out integrally with the originalplates of the base, as shown in the methods of producingpiezoelectric/electrostrictive devices 10 a to 10 h. This allowspiezoelectric/electrostrictive elements 21 to 24 having a shape shown inFIG. 11 or FIG. 12 to be formed integrally on the original plate of thebase.

Here, it is preferable to perform a surface roughening treatment such asblasting, etching, or plating in advance on the surface site of the basewhere the piezoelectric/electrostrictive element is to be bonded. Byallowing the surface roughness of the bonding site to be Ra=about 0.1 μmto 5 μm, the bonding area can be increased to improve the adhesivestrength. In this case, the surface of the bonding site on thepiezoelectric/electrostrictive element side is preferably rough as well.If one wishes that the electrodes are not electrically conducted to thebase, the electrodes are not disposed on the surface of thepiezoelectric/electrostrictive layer constituting the lowermost layer.

If solder or brazing material is to be used as the adhesive, it ispreferable to dispose an electrode layer made of a metal material on thesurface of the piezoelectric/electrostrictive element in order toimprove the wettability. The thickness of the adhesive is preferablywithin the range from 1 μm to 50 μm. The thickness of the adhesive ispreferably small in view of reducing dispersions in the displacement andin the resonance c characteristics of the, device and in view of savingspace; however, in order to ensure the characteristics such as thebonding strength, displacement, and resonance, the optimal thickness isset for each adhesive to be adopted.

The selection in the case of adopting piezoelectric/electrostrictiveelements 21 to 24 in piezoelectric/electrostrictive devices 10 a to 10 haccording to each embodiment is carried out on the basis of an intendedusage of piezoelectric/electrostrictive devices 10 a to 10 h. In apiezoelectric/electrostrictive element having a small number of layersconstituting the piezoelectric/electrostrictive layer, the driving forceis small and the power consumption is small. Conversely, in apiezoelectric/electrostrictive element having a large number of layersconstituting the piezoelectric/electrostrictive layer, the driving forceis large and the power consumption is large. In consideration of thesefacts, one selects a piezoelectric/electrostrictive element suitable forthe intended usage of the piezoelectric/electrostrictive device.Generally, the piezoelectric/electrostrictive element preferably has aplurality of layers constituting the piezoelectric/electrostrictivelayer, and one can suitably adopt a piezoelectric/electrostrictiveelement having three layers to ten layers constituting thepiezoelectric/electrostrictive layer. The shift in the position of theelectrodes in the piezoelectric/electrostrictive element is preferablyat most 50 μm.

EXAMPLES

In this Example, a piezoelectric/electrostrictive device belonging tothe category of the second piezoelectric/electrostrictive device 10 bshown in FIG. 1B and constituting the second embodiment of the presentinvention is prepared, and the piezoelectric/electrostrictive device israised as a representative example of the piezoelectric/electrostrictivedevice according to the present invention. On the basis of thepiezoelectric/electrostrictive device, detailed description will begiven on the construction, operation, functions, and effects of thepiezoelectric/electrostrictive device according to the presentinvention. FIG. 13 is a plan view of the piezoelectric/electrostrictivedevice.

The piezoelectric/electrostrictive device 30 is made of a base 31 and apair of piezoelectric/electrostrictive elements 32. For each of thepiezoelectric/electrostrictive elements 32, apiezoelectric/electrostrictive element 24 shown in FIG. 12B is adopted.Therefore, in the following description of each construction member ofthe piezoelectric/electrostrictive element 32, the reference symbols ofthe construction members of the piezoelectric/electrostrictive element24, which are accompanied by the number 24, will be changed to thecorresponding reference symbols accompanied by the number 32 for use.

Base 31 constituting the piezoelectric/electrostrictive device 30 has anopen-box shape made of a pair of movable parts 31 a, 31 b that arearranged in parallel with each other to oppose each other and aconnecting part 31 c that connects the two movable parts 31 a, 31 b witheach other at one end thereof. The two movable parts 31 a, 31 b and theconnecting part 31 c are integrally formed with one sheet of band-shapedflat plate. Base 31 is open to the other end of the two movable parts 31a, 31 b, and the inside surfaces at the other end of the two movableparts 31 a, 31 b are formed to be mounting sites 31 a 1, 31 b 1 formounting a component H such as a magnetic head.

Piezoelectric/electrostrictive elements 32 are bonded onto the outerside surfaces at the other end of movable parts 31 a, 31 b, and extendfor a predetermined length from the other end of movable parts 31 a, 31b towards the one end. Further, the two ends of component H are fixedonto the mounting sites 31 a 1, 31 b 1 of movable parts 31 a, 31 b viaadhesives 31 a 2, 31 b 2.

The dimensions of the sites of base 31 constituting thepiezoelectric/electrostrictive device 30 and the sites ofpiezoelectric/electrostrictive elements 32 are set to be the optimaldimensions in consideration of the supporting strength of the twomovable parts 31 a, 31 b to component H, the amount of displacementimparted to component H by the two movable parts 31 a, 31 b, and otherfactors.

In the piezoelectric/electrostrictive device 30, base 31 is formed, forexample, with SUS304 having a plate thickness of 40 μm. Further, aspiezoelectric/electrostrictive element 32,piezoelectric/electrostrictive element 24 shown in FIG. 12B is adopted,and is a four-layer structure in which PZT is used. The thickness ofeach layer of piezoelectric/electrostrictive layers 32 a is 15 μm.Electrodes 32 b, 32 c are made of platinum of 3 μm, and terminals 32 d,32 e are thin films made of gold paste. Piezoelectric/electrostrictiveelements 32 are bonded onto outer sides of movable parts 31 a, 31 b viaa one-liquid thermosetting epoxy resin adhesive.

In the piezoelectric/electrostrictive device 30 having such aconstruction, the displacement of mounting sites 31 a 1, 31 b 1 inmovable parts 31 a, 31 b was measured whenpiezoelectric/electrostrictive element 32 was driven by a sinusoidalwave of 1 kHz with a driving voltage of 20±20V. The displacement wasfound to be ±1.5 μm. Further, the resonance frequency showing themaximum value of displacement was measured by sweeping the frequency atsinusoidal wave voltage ±0.5 V, and was found out to be 45 kHz.

Next, the operation of the piezoelectric/electrostrictive deviceaccording to the present invention will be described with reference tothe above-described piezoelectric/electrostrictive device 30. FIG. 13shows the piezoelectric/electrostrictive device 30 in a non-operatingstate, and FIG. 14 shows the piezoelectric/electrostrictive device 30 inan operating state.

The piezoelectric/electrostrictive device 30 is in a state shown in FIG.13 at the time of non-operation when a voltage is not applied topiezoelectric/electrostrictive elements 32. In this state, thelongitudinal axis m of piezoelectric/electrostrictive device 30 isalmost coincident with the central axis n between mounting sites 31 a 1,31 b 1. In this state, a sinusoidal wave Wb having a predetermined biasvoltage Vb is applied to the pair of electrodes 32 b, 32 c in onepiezoelectric/electrostrictive element 32, for example, as shown in thewaveform diagram of FIG. 15A, and a sinusoidal wave Wa having a phasedifferent by approximately 180° from that of the aforesaid sinusoidalwave Wb is applied to the pair of electrodes 32 b, 32 c in the otherpiezoelectric/electrostrictive element 32, for example, as shown in FIG.15B.

This allows that, at the stage when for example the maximum voltage isapplied to the pair of electrodes 32 b, 32 c in the onepiezoelectric/electrostrictive element 32, thepiezoelectric/electrostrictive layers 32 a in the onepiezoelectric/electrostrictive element 32 undergo shrinking displacementin the principal surface direction thereof. This generates a stress thatwarps one movable part 31 a of base 31 in the illustrated rightdirection (direction shown by arrow A) in thepiezoelectric/electrostrictive device 30, for example, as shown in FIG.14. By this stress, movable part 31 a is warped in that direction.

In this case, the pair of electrodes 32 b, 32 c in the otherpiezoelectric/electrostrictive element 32 are in a state in which avoltage is not applied. Therefore, the other movable part 31 b of base31 follows the warp of the one movable part 31 a so as to warp in thesame direction as that of movable part 31 a. As a result of this,movable parts 31 a, 31 b both displace in the illustrated rightdirection with respect to the longitudinal axis m ofpiezoelectric/electrostrictive device 30. The displacement amount ofthis displacement changes in accordance with the maximum value of thevoltage applied to each of the piezoelectric/electrostrictive elements32. The larger the maximum value of the voltage is, the larger thedisplacement amount will be.

In particular, if a piezoelectric/electrostrictive material having ahigh coercive electric field is adopted as a material for constructingthe piezoelectric/electrostrictive layers 32 a constituting thepiezoelectric/electrostrictive element 32, the aforesaid bias voltagemay be adjusted so that the minimum level will be at a slightly negativelevel, as illustrated by waveforms drawn in two-dot chain lines in FIGS.15A and 15B. In this case, by driving the piezoelectric/electrostrictiveelement to which the bias voltage of negative level is applied, forexample, by driving the other piezoelectric/electrostrictive element 32,for example, a stress is generated in the other movable part 31 b ofbase 31 in the same direction as the warping direction of the onemovable part 31 a, thereby providing a larger displacement amount ofmounting sites 31 a 1, 31 b 1.

In other words, by using the waveforms shown in two-dot chain lines inFIGS. 15A and 15B, the piezoelectric/electrostrictive element 32 towhich the bias voltage of negative level is applied can have a functionof supporting the piezoelectric/electrostrictive element 32 acting as amain agent of displacement operation.

Thus, in the piezoelectric/electrostrictive device 30, a minutedisplacement of piezoelectric/electrostrictive elements 32 is amplifiedto become a large displacement operation by utilizing the warp of thetwo movable parts 31 a, 31 b of base 31, and is transmitted to the twomovable parts 31 a, 31 b. This makes it possible to displace themounting sites 31 a 1, 31 b 1 to a great extent with respect to thelongitudinal axis m of piezoelectric/electrostrictive device 30.

In the piezoelectric/electrostrictive device 30, it is preferable togive the following consideration to the dimension relationship of thesites of base 31 and the sites of piezoelectric/electrostrictiveelements 32 so that the functions thereof will be exhibited with morecertainty.

FIG. 13 shows the dimensions of the sites in thepiezoelectric/electrostrictive device 30. In the dimensions, L1represents the total length of piezoelectric/electrostrictive device 30and is the total length of base 31, and L2 represents the total width ofpiezoelectric/electrostrictive device 30. Further, L3 represents thetotal width of base 31; L4 represents the interval between the twomovable parts 31 a, 31 b of base 31; L5 represents the length ofnon-bonded sites of piezoelectric/electrostrictive elements 32 inmovable parts 31 a, 31 b; L6 represents the length ofpiezoelectric/electrostrictive elements 32; and L7 represents the widthof piezoelectric/electrostrictive elements 32.

Furthermore, in the dimensions, L8 represents the length of theoverlapping portion between the substantial driving part of thepiezoelectric/electrostrictive elements and the fixing part of thecomponent mounting part; L9 is the thickness of the adhesive; L10 is thethickness of the movable parts; L11 is the thickness of the connectingpart; L12 is the length of the movable sites in the movable parts; L13is the length of the bonding surface of the mounting parts; L14 is thelength of the substantial driving part of piezoelectric/electrostrictiveelements 32; M1 is the length of component H; and M2 is the width ofcomponent H.

In the piezoelectric/electrostrictive device 30, the relationshipbetween the interval L4 of the two movable parts 31 a, 31 b of base 31and the lateral length M1 of component H is such that L4≧M1, andL4−M1=0.001 to 0.01 mm. If L4<M1, it is necessary to enlarge the gapbetween the two movable parts 31 a, 31 b in inserting component Hbetween the two movable parts 31 a, 31 b, and there is a fear ofbreaking the device in enlarging the gap. The thickness L9 of theadhesive is from 0.005 to 0.1 mm, more preferably from 0.01 to 0.05 mm.If the thickness L9 of the adhesive is larger than 0.1 mm, the adhesiveis liable to flow out, making it difficult to insert the adhesive intothe thickness of a predetermined dimension.

If the difference between the interval L4 of the two movable parts 31 a,31 b of base 31 and the lateral length M1 of component H is small, it isdifficult to insert component H into the interval L4 and also it isdifficult to inject the adhesive between component H and the mountingsites 31 a 1, 31 b 1, making it difficult to control the thickness L9 ofthe adhesive. If the thickness L9 of the adhesive is set to be smallerthan 0.01 mm, dispersions are liable to occur in the bonding strength tocomponent H. For this reason, the thickness L9 of the adhesive is morepreferably from 0.01 to 0.03 mm.

The thickness L10 of movable parts 31 a, 31 b of base 31 is from 0.001to 0.2 mm, more preferably from 0.01 to 0.1 mm, still more preferablyfrom 0.03 to 0.08 mm. The total width (length) L2 of connecting part 31c, the length L12 of the movable sites of movable parts 31 a, 31 b, thethickness L9 of the adhesive of mounting sites 31 a 1, 31 b 1, thethickness L10 of movable parts 31 a, 31 b, and others are preferably assmall as possible. This reduces the total length L1 and the total widthL2 of the device, leading to scale reduction of the device.

The length L12 of the movable sites of movable parts 31 a, 31 b in base31 is from 0.2 to 3 mm, preferably from 0.3 to 2 mm. The length L13 ofmounting sites 31 a 2, 31 b 2 of the two movable parts 31 a, 31 b isfrom 0.05 to 2 mm. The interval L4 of the two movable parts 31 a, 31 bis from 0.1 to 2 mm, preferably from 0.2 to 1.6 mm. With this dimension,the ratio of (length L3 of the two movable parts 31 a, 31 b)/(intervalL4 of the two movable parts 31 a, 31 b) is from 0.5 to 10, preferablyfrom 0.5 to 5. The ratio of (interval L4 of the two movable parts 31 a,31 b)/(thickness L10 of movable parts 31 a, 31 b) is from 0.5 to 20,preferably from 1 to 15, more preferably from 1 to 10.

The length L8 of the overlapping portion between the substantial drivingpart of the piezoelectric/electrostrictive elements and the fixing partof the component mounting part is preferably larger than ½ of thethickness L10 of movable parts 31 a, 31 b, namely, L8>(L10/2). With suchsetting, the driving force of piezoelectric/electrostrictive layers 32 awill act efficiently on the displacement.

In the state shown in FIG. 13, the length L13 of the bonding surface ofmounting sites 31 a 1, 31 b 1 in movable parts 31 a, 31 b of the base isset to be approximately equal to the width M2 of component H. However,if the length M1 of component H is larger than the width M2 thereof, inorder not to increase the length L13 of mounting sites 31 a 1, 31 b 1,one can form mounting sites 31 a 1, 31 b 1 to have a bonding-definedlength (length defined by bonding or length needed for bonding) asillustrated in device 10 f, whereby the length L13 of the bondingsurface of mounting sites 31 a 1, 31 b 1 is defined independently fromthe width M2 of component H. Alternatively, one can allow the tip end ofcomponent H to protrude from mounting sites 31 a 1, 31 b 1 in a state inwhich component H is bonded.

The length L14 of the substantial driving part of thepiezoelectric/electrostrictive elements is preferably from 20 to 95,more preferably from 40 to 80, of the length L12 of the movable sites inmovable parts 31 a, 31 b.

The piezoelectric/electrostrictive device 30 can be used, for example,as an actuator for controlling a magnetic head, or as an accelerationsensor.

In the case where the piezoelectric/electrostrictive device 30 is to beused as an actuator for controlling a magnetic head, component H shownin FIG. 13 is a magnetic head, and the piezoelectric/electrostrictivedevice 30 at connecting part 31 c of base 31 thereof is fixed to asuspension. The suspension is a supporting base for supporting thepiezoelectric/electrostrictive device 30, and thepiezoelectric/electrostrictive device 30 in a state of being fixed tothe suspension is in a state in which the sites other than theconnecting part 31 c thereof are floating above the suspension.

Further, in the case where the piezoelectric/electrostrictive device 30is to be used as an acceleration sensor, component H shown in FIG. 13 isa weight, and the weight H is bonded to mounting sites 31 a 1, 31 b 1 inthe two movable parts 31 a, 31 b of base 31. FIG. 16 shows a mode inwhich the piezoelectric/electrostrictive device 30 is used as anacceleration sensor S, and FIG. 17 shows a state before assembling asthe acceleration sensor S.

In the acceleration sensor S, weight H is bonded onto mounting sites 31a 1, 31 b 1 of the two movable parts 31 a, 31 b with the use of anadhesive such as an epoxy resin, and the piezoelectric/electrostrictivedevice 30 at connecting part 31 c thereof is fixed to a mounting site s2of a wiring substrate s1 via an adhesive such as an epoxy resin. Thepiezoelectric/electrostrictive device 30 in this mounting state is in astate in which the sites other than the connecting part 31 c thereof arefloating above the wiring substrate s1. Here, on the wiring substrate s1are formed wirings for electrical connection and various circuits,illustration of which is omitted.

In the acceleration sensor S, bonding of thepiezoelectric/electrostrictive device 30 to wiring substrate s1 can becarried out using spot welding or the like. If spot welding is adoptedas bonding means, the bonding area will be small, and thepiezoelectric/electrostrictive device 30 can be firmly fixed onto wiringsubstrate s1. Further, by suitably setting the mass of weight H, thesensitivity in sensing the acceleration can be adjusted.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous othermodifications and variations can be devised without departing from thescope of the invention.

1. A piezoelectric/electrostrictive device comprising a base having apair of movable parts that are arranged in parallel with each other tooppose each other, a connecting part that connects the two movable partswith each other at one end thereof, and a piezoelectric/electrostrictiveelement disposed on an outer side surface of at least one of said twomovable parts in the base, wherein said base is integrally constructedwith one sheet of a band-shaped flat metal plate, and said movable partsextend for a predetermined length from respective ends of saidconnecting part to other ends.
 2. The piezoelectric/electrostrictivedevice as claimed in claim 1, wherein saidpiezoelectric/electrostrictive element is shorter than said movableparts and is positioned at the other end of said movable parts.
 3. Thepiezoelectric/electrostrictive device as claimed in claim 1, whereinsaid piezoelectric/electrostrictive element is shorter than said movableparts and is positioned at the one end of said movable parts.
 4. Thepiezoelectric/electrostrictive device as claimed in claim 1, whereinsaid base has a generally open-box shape that is open to the other endof said two movable parts.
 5. The piezoelectric/electrostrictive deviceas claimed in claim 4, wherein said base includes a flat plate partdisposed on an inner surface or on an outer surface of said connectingpart.
 6. The piezoelectric/electrostrictive device as claimed in claim1, wherein said base has a generally horseshoe shape that is open to theother end of said two movable parts.
 7. Thepiezoelectric/electrostrictive device as claimed in claim 1, whereinconnecting sites between the ends of the connecting part and the movableparts constituting said base are formed as recesses having a circulararc shape.
 8. The piezoelectric/electrostrictive device as claimed inclaim 1, wherein the movable parts of said base include thinned portionslocated in a middle of a length thereof.
 9. Thepiezoelectric/electrostrictive device as claimed in claim 1, which isused in a mode in which a component to be controlled or tested issandwiched between inner surfaces of the other ends of said two movableparts constituting said base.
 10. A method of producing a baseconstituting a piezoelectric/electrostrictive device as claimed in claim1, comprising the steps of: preparing a flexible and bendable flat plateas a material for forming said base; cutting the flat plate into flatplates each having a shape that delineates a planar development of saidbase thereby to form original plates having a narrow strip shape; andbending each of the original plates at predetermined sites to form saidbase integrally having said two movable parts and said connecting part.11. A method of producing a piezoelectric/electrostrictive device asclaimed in claim 1, comprising the steps of: preparing a flexible andbendable flat plate as a material for forming said base; cutting theflat plate into flat plates each having a shape that delineates a planardevelopment of said base thereby to form original plates having a narrowstrip shape; bending each of the original plates at predetermined sitesso as to form said base integrally having said two movable parts andsaid connecting part; and bonding a piezoelectric/electrostrictiveelement onto an outer side surface of at least one of the two movableparts constituting the base thereby to form thepiezoelectric/electrostrictive device.
 12. A method of producing apiezoelectric/electrostrictive device as claimed in claim 1, comprisingthe steps of: preparing a flexible and bendable flat plate as a materialfor forming said base, said flat plate having apiezoelectric/electrostrictive element bonded thereto at a predeterminedsite in advance; cutting the flat plate integrally with saidpiezoelectric/electrostrictive element into flat plates each having ashape that delineates a planar development of said base thereby to formoriginal plates having a narrow strip shape; and bending each of theoriginal plates at predetermined sites to form said base integrallyhaving said two movable parts and said connecting part and to form thepiezoelectric/electrostrictive device having thepiezoelectric/electrostrictive element bonded onto an outer side surfaceof at least one of said two movable parts.
 13. A method of producing abase constituting a piezoelectric/electrostrictive device as claimed inclaim 1, comprising the steps of: preparing a flexible and bendable flatplate as a material for forming said base; cutting the flat plate intoflat plates each having a shape that delineates a planar development ofsaid base thereby to form original plates having a narrow strip shape;and bending each of the original plates at predetermined sites to formsaid base integrally having said two movable parts and said connectingpart.